M5-no Dsp Audio Out

Question

My M5 started doing the "blue screen" where it never came on despite having the Line6 power supply. I actually dug out a power supply that put out 3 amps at the correct voltage just to double check that wasn't the problem. I removed a baseplate screw, scraped the case paint and replaced with a bare metal screw as suggested elsewhere-that solved the "on" problem. I can now reliably get the pedal to power on. It has, however, stopped passing audio in DSP mode (either bypass or effect on). In true bypass mode it will pass signal, so I've got to think the switch is OK. I've done a factory reset, and reloaded the firmware twice to no avail. Aside from disassembling it to see if there's a faulty ribbon cable, any other thoughts?